More evidence of a Sept. 21 launch for Apple's next iPhone has come from mail carrier FedEx, which has begun alerting employees about a "surge volume" event beginning that Friday.

FedEx has postponed a corporate class in anticipation of the unnamed event that will occur from Sept. 21 through 24, according to a company memo published on Friday by MacRumors. The company is also said to be limiting employee travel during the four-day span.

Apple typically partners with FedEx for home deliveries of its new product launches. And the date cited by FedEx aligns with previous rumors pointing toward a Sept. 21 launch date after next Wednesday's media event.

Sept. 21 is a Friday, which is the day of the week Apple traditionally uses for product releases. Last year, Apple announced the iPhone on Tuesday, Oct. 4, and the device launched the following week on Friday, Oct. 14.

Following a similar pattern this year, Apple is expected to unveil its next-generation iPhone, referred to unofficially as the "iPhone 5," at its event next Wednesday, Sept. 12, with the product officially launching the following Friday.

Apple's special event invitations sent out this week hint at the iPhone 5. Image viaThe Loop.

The new iPhone is expected to be the biggest product launch in Apple's history, which would explain why FedEx is adjusting its corporate schedule accordingly. In March, an overwhelming number of preorders for Apple's third-generation iPad led to delayed shipments through both FedEx and UPS.

Apple's "It's Almost Here" media event kicks off next Wednesday at 10 a.m. Pacific, 1 p.m. Eastern from the Yerba Buena Center for the Arts in San Francisco, Calif. AppleInsider will have full, live coverage of the presentation.